Department of Molecular Biology and Biotechnology, Faculty of Biology and Geology, 5-7 Clinicilor Street, 400006, Cluj-Napoca, Romania.
Emil G. Racoviță Institute, Babeș-Bolyai University, 5-7 Clinicilor Street, 400006, Cluj-Napoca, Romania.
Extremophiles. 2022 Jun 28;26(2):21. doi: 10.1007/s00792-022-01266-z.
Members of candidate Asgardarchaeota superphylum appear to share numerous eukaryotic-like attributes thus being broadly explored for their relevance to eukaryogenesis. On the contrast, the ecological roles of Asgard archaea remains understudied. Asgard archaea have been frequently associated to low-oxygen aquatic sedimentary environments worldwide spanning a broad but not extreme salinity range. To date, the available information on diversity and potential biogeochemical roles of Asgardarchaeota mostly sourced from marine habitats and to a much lesser extend from true saline environments (i.e., > 3% w/v total salinity). Here, we provide an overview on diversity and ecological implications of Asgard archaea distributed across saline environments and briefly explore their metagenome-resolved potential for osmoadaptation. Loki-, Thor- and Heimdallarchaeota are the dominant Asgard clades in saline habitats where they might employ anaerobic/microaerophilic organic matter degradation and autotrophic carbon fixation. Homologs of primary solute uptake ABC transporters seemingly prevail in Thorarchaeota, whereas those putatively involved in trehalose and ectoine biosynthesis were mostly inferred in Lokiarchaeota. We speculate that Asgardarchaeota might adopt compatible solute-accumulating ('salt-out') strategy as response to salt stress. Our current understanding on the distribution, ecology and salt-adaptive strategies of Asgardarchaeota in saline environments are, however, limited by insufficient sampling and incompleteness of the available metagenome-assembled genomes. Extensive sampling combined with 'omics'- and cultivation-based approaches seem, therefore, crucial to gain deeper knowledge on this particularly intriguing archaeal lineage.
候选的 Asgardarchaeota 超门成员似乎具有许多类似真核生物的属性，因此它们在真核生物起源方面得到了广泛的研究。相比之下，Asgard 古菌的生态作用仍未得到充分研究。Asgard 古菌经常与世界各地低氧水生沉积物环境有关，其盐度范围较宽但不极端。迄今为止，关于 Asgardarchaeota 的多样性和潜在生物地球化学作用的可用信息主要来自海洋生境，而从真正的咸水环境（即总盐度>3%w/v）获得的信息要少得多。在这里，我们概述了分布在咸水环境中的 Asgard 古菌的多样性和生态意义，并简要探讨了它们通过宏基因组解析的渗透适应潜力。Loki、Thor 和 Heimdallarchaeota 是在咸水栖息地中占优势的 Asgard 进化枝，它们可能利用厌氧/微需氧有机物降解和自养碳固定。Thorarchaeota 中似乎存在主要溶质摄取 ABC 转运蛋白的同源物，而推测涉及海藻糖和章鱼胺生物合成的同源物则主要在 Lokiarchaeota 中推断出来。我们推测，Asgardarchaeota 可能采用相容溶质积累（“盐析”）策略来应对盐胁迫。然而，由于采样不足和可用宏基因组组装基因组的不完整性，我们目前对 Asgardarchaeota 在咸水环境中的分布、生态学和盐适应策略的理解是有限的。因此，广泛的采样结合“组学”和培养方法似乎对于深入了解这个特别有趣的古菌谱系至关重要。
